Don't require GOPATH for development (#3061)
Don't require GOPATH for development (#3061)

With modules, GOPATH is  not commonly used by Go developers anymore. Switch to the non-GOPATH instructions.
open-telemetry/opentelemetry-collector,open-telemetry/opentelemetry-collector,open-telemetry/opentelemetry-collector-contrib,open-telemetry/opentelemetry-collector-contrib,open-telemetry/opentelemetry-collector